The study has shown that the dendrites themselves are highly active, sending spikes of their own at a rate 10 times that previously believed. “Dendrites make up more than 90 percent of neural tissue,” said UCLA neurophysicist Mayank Mehta, the study’s senior author.
The researchers also found that unlike the spikes of electrical activity generated by the somas, the dendrites could put out longer-lasting voltages that in their sum total were actually more powerful than the somatic spikes.
“A fundamental belief in neuroscience has been that neurons are digital devices. They either generate a spike or not. These results show that the dendrites do not behave purely like a digital device. Dendrites do generate digital, all-or-none spikes, but they also show large analog fluctuations that are not all or none. This is a major departure from what neuroscientists have believed for about 60 years.”
Mehta adds that the fact that dendrites are about 100 times larger in volume than somas, it’s possible that our brains have 100 times more capacity to compute information than previously believed.
They found that the dendrites were five times more active than the somas when the rats were sleeping, and 10 times more active when they were awake and moving about.
“Our findings indicate that learning may take place when the input neuron is active at the same time that a dendrite is active – and it could be that different parts of dendrites will be active at different times, which would suggest a lot more flexibility in how learning can occur within a single neuron.”